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Hello everyone!
 
I have some issues with the GC, and how it works.
 
First I try to run the following script. It reached the max 512m RES memory usage, and drops to 1000b just after collectgarbage call. 
 
local clock = os.clock
 t = {}
 t[1] = {}
 for i=0, 20000000 do
 table.insert(t[1],i)
end
print ("Heap Size1:" .. collectgarbage('count')/1024)
t[1] = nil
 print ("Done.")
 collectgarbage("collect")
print ("Heap Size2:" .. collectgarbage('count')/1024)
local t0 = clock()
while clock() - t0 <= 30 do end
 
 
Top
 
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
17909 mozturk   25   0  527m 512m  684 R 99.4  0.2   0:07.17 lua

  
 
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
20090 mozturk   25   0 15368 1000  752 R 98.6  0.0   0:10.54 lua

Prints:
 
Heap Size1:512.028673172
Done.
Heap Size2:0.026923179626465
 
 
Second when I just change "i" to "{i}" (mark it bold) which I really wanted (I minimize the code for clearity.) the RES memory goes up to 2.6g and drops to 2.1g just after collectgarbage call.
 
local clock = os.clock
 t = {}
 t[1] = {}
 for i=0, 20000000 do
 table.insert(t[1],{i})
end
print ("Heap Size1:" .. collectgarbage('count')/1024)
t[1] = nil
 print ("Done.")
 collectgarbage("collect")
print ("Heap Size2:" .. collectgarbage('count')/1024)
local t0 = clock()
while clock() - t0 <= 30 do end
 
 

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
25207 mozturk   25   0 2663m 2.6g  736 R 98.6  1.0   0:21.81 lua


  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
25207 mozturk   25   0 2663m 2.1g  736 R 98.6  1.0   0:21.81 lua

Prints:
 
Heap Size1:2037.9059820175
Done.
Heap Size2:0.026938438415527

 
The question is why do GC reports different than os system. Why doesn't it reclaim the pyhsical memory?
 
Best Regards.
 
System info:
 
[mozturk@pacific bin]$ ./lua
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
>
[mozturk@pacific bin]$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-libgcj-multifile --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --enable-plugin --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --with-cpu=generic --host=x86_64-redhat-linux
Thread model: posix
gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)
[mozturk@pacific bin]$ uname -a
Linux pacific 2.6.18-194.el5 #1 SMP Tue Mar 16 21:52:39 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux